Measurement system for improved paper roll runnability

ABSTRACT

A system for measuring both caliper and tension of a web such as paper wound into a roll. The system may include a standard caliper sensor whose air supply is selectively modified to allow for both the measurement of caliper and tension of the web. In another embodiment two similar or identical measurement devices are installed in tandem where one device measures tension without pinching the sheet and the other device measures caliper. The sensor may include two sheet guides for providing support for tension measurement or one or both sheet guides can be eliminated by support from machinery rolls.

1. FIELD OF THE INVENTION

This invention relates to paper rolls and more particularly to therunnability of a paper roll.

2. DESCRIPTION OF THE PRIOR ART

Paper products are typically shipped in large rolls from the paper millto a converting or printing facility.

The paper quality can be characterized by sheet properties, for instancethickness, basis weight, moisture content or strength, but there areadditional mechanical properties of the paper roll as an entity that areequally important for the user. These additional mechanical propertiesare often referred to as “roll runnability”, designating how well theroll unwinds and pulls though the process, and the flatness anduniformity of the resulting web. For instance, if there is a localtension variability in the roll, the resulting web may become locallywrinkled or tend to pull diagonally instead of straight, or even breakat localized high tension areas.

Rolls from different paper machines or made at different times orlocations of a machine may have different runnability characteristics.For example, some rolls may tend to pull diagonally left and other rollsmay tend to pull right. The converting or printing machinery may in somecases be adjusted to partially correct for a particular runnabilitycondition, but that machinery cannot economically be re-adjusted betweenrolls.

There is thus a rising concern in converting plants and at printinghouses, that, because of the roll runnability characteristics, differentpaper rolls delivered from different paper machines may result in poorend product quality and sheet breaks. Runnability problems of a paperroll may occur despite acceptable test values for sheet qualityproperties in each roll of paper. Therefore, it is desirable to betterquantify runnability properties of rolls.

Several methods have been suggested to measure and control runnabilityquality of paper rolls. On-line paper reel hardness sensors were on themarket in the 1970's. This included the “Back Tender's Friend”,utilizing a design originated by Consolidated-Bathurst, Inc., and builtby a few gauging suppliers including AccuRay Corporation, now part ofABB, and similar solutions that mechanically inspect the reel as it isbeing built. These reel mechanical inspection solutions measure thelocal roll hardness by the force impulse generated by a contacting andtraversing small roller sensing device in contact with the rollperiphery including piezoelectric signal transducers that can estimatethe hardness profile. These reel mechanical inspection solutions addcost and complexity to the papermaking process.

Improved caliper sensors came on the market in the 1980's and 1990's andenabled closed loop caliper profile control. One example of an improvedcaliper sensor is disclosed in U.S. Pat. No. 5,479,720 (“the '720patent”) which is assigned to the assignee of the present invention andthe disclosure of which is hereby incorporated herein by reference.Similar devices are now standard equipment on many paper machines. Byautomatic control of the caliper profile, reel building improves due toa more uniform contact surface between the layers of paper. However,caliper information only is not adequate to predict the mechanicalrunnability properties of a paper roll being built. The web tension isalso essential.

The total web tension is today easily measured via motor torque or viaload cells on lead rolls for the paper web. This information can be usedto control the roll building process for proper nominal tension.

However, the tension has a cross directional profile.

Portions of the web may be slack and other portions may have hightension streaks. If the tension is not uniform across the web, the sheetwill not wind in a proper cylindrical shape and the non-uniform tensionwill cause ridges, wrinkles and hard versus soft areas in the paperroll. The reasons for an uneven web tension profile includes a CDdependent fiber orientation, pressing, drying and rewetting of thepaper. Cross machine moisture control to level the moisture profile atthe reel may not always help and in some cases worsen the tensionprofile by shrinking or expanding the sheet dimensions.

Good reel building is particularly difficult on thin or moderatethickness paper grades due to a large number of wraps and low bendingstiffness of the sheet.

A stand-alone web tension profile sensor can be produced by installing astationary beam where the sheet wraps around stationary sensing devices,for instance an array of air orifices. This is described in U.S. Pat.No. 5,052,233. Drawbacks of these devices include high cost, extra spaceneeded in the paper machine, and impairing threading of the paper.Additionally, the signal handling to combine tension and caliperinformation for a roll quality estimate becomes complex.

Another solution of including multiple caliper sensors each pinching thesheet from both sides, and utilized for web tension measurement andcorrection for a contacting sheet stiffness sensor has been suggested.

This is described in U.S. Pat. No. 5,029,469. This solution is complex,and it did not generate much success.

Due to the general industry acceptance of modern caliper sensors, thereis today a caliper sensor on virtually every paper machine where reelbuilding is essential. The present invention shares this caliper sensorhardware for reel tension measurement and merges the caliper and tensioninformation into a prediction of roll hardness uniformity.

SUMMARY OF THE INVENTION

A method for measuring in a direction across a moving web both tensionand caliper of the moving web comprising:

using a single sensor to measure tension and caliper of the moving webat a location on the moving web;

providing support for the moving web before and after the location onthe moving web where the single sensor measures tension and caliper ofthe moving web; and

controlling the single sensor to alternate between two operating modeswhere in one of the two operating modes the single sensor measurescaliper of the moving web and in another of the two operating modes thesingle sensor measures tension of the moving web.

A single sensor for measuring in a direction across a moving web bothtension and caliper of the moving web at a location on the moving webcomprising:

-   -   means for operating the single sensor to alternate between the        caliper measurement and the tension measurement.

A method for measuring in a direction across a moving web both tensionand caliper of the moving web comprising:

using two sensors in tandem to measure at a location on the moving webtension of the moving web by one of the two sensors and caliper of themoving web by another of the two sensors.

A system for measuring at a location on a moving web both caliper andtension of the moving web comprising:

a sensor for measuring caliper of the moving web in tandem with a sensorfor measuring tension of the moving web;

at least one guide associated with the sensor for measuring tension ofthe moving web to support the moving web during the tension measurement.

A quality control system for a web making machine comprising:

a scanning frame having an opening through which a moving web passes;

a sensor mounted in the scanning frame for measuring at locations acrossthe moving web both tension and caliper of the moving web, the scanningframe operable to cause the sensor to move back and forth across themoving web; and

means for operating the sensor to alternate between the calipermeasurement and the tension measurement.

A web making machine comprising:

a system for controlling quality of the web comprising:

a scanning frame having an opening through which a moving web passes;

a sensor mounted in the scanning frame for measuring at locations acrossthe moving web both tension and caliper of the moving web, the scanningframe operable to cause the sensor to move back and forth across themoving web; and

means for operating the sensor to alternate between the calipermeasurement and the tension measurement.

DESCRIPTION OF THE DRAWING

FIG. 1 shows a schematic view of winding a reel from a web material.

FIG. 2 shows a conventional paper making machine including the caliperand tension measuring system of the present invention.

FIG. 3 shows a prior art caliper sensor.

FIG. 4 shows the prior art caliper sensor and air supply modified inaccordance with the present invention.

FIG. 5 shows the sensor of FIG. 4 activated to measure web tension.

FIG. 6 shows another embodiment for the caliper and tension measuringsystem of the present invention.

FIG. 7 shows a further embodiment for the caliper and tension measuringsystem of the present invention.

FIG. 8 shows the fundamental tension measuring geometry.

FIG. 9 shows a graph of tension versus vertical deflection.

FIG. 10 shows a graph of force versus paper thickness.

DETAILED DESCRIPTION

As is illustrated in FIG. 1, the qualities of a wound paper roll 16 aresignificantly influenced by the web CD caliper profile, the CD tensionprofile, and well as the overall tension level in the MD. An un-evencaliper CD profile causes layers of paper to contact at high thicknessCD locations and to have loose contact or air gaps at low thicknesslocations. With a relatively stable CD profile, the errors accumulatedue to a very large number of wraps in a large diameter paper roll. Theaccumulated errors may result in a non cylindrical shape and localizedhard and soft areas on the roll. The effect of uneven thickness profileis often worse on thin paper grades where the number of wraps becomelarge. For instance, a full newsprint reel in a paper machine may have15,000 wraps of paper.

The other important factor for roll building is the web tension. Thishas two components—the tension CD profile and the overall MD tension.The CD profile may be caused by un-even drying or re-moisturizing of thepaper web in the CD direction, un-even fiber orientation from the wetend, and related shrinkage effects. As illustrated in FIG. 1, overall MDtension can be managed by motor drive controls 18 which includescontroller 18 a and drive motor 18 b. The CD profile superimposeslocalized high tension or low tension areas of the paper windingprocess. The tension profile may cause hard spots or soft spots on thereel, or tendency to skew the web, web overstressing and even failure athigh tension areas.

FIG. 2, which is FIG. 1 of the '720 patent, shows a conventional papermaking machine 10 having final calendering rolls 11 and associated crossmachine control actuators 11 a. A caliper and tension measuring system 5constructed in accordance with the present invention is preferablypositioned downstream from the final calendering rolls 11 and isadvantageously used to monitor the thickness and tension of a movingsheet of paper 12 after the final calendering operation.

The caliper and tension measuring system 5 includes a scanning station20. The moving sheet of paper 12 can be seen passing through thescanning station 20 between upper and lower transverse beams 22 and 24on which are mounted upper and lower sensing heads 30 and 50. Thesensing heads 30 and 50 are driven back and forth across the width ofthe paper 12 in a continuous scanning motion, keeping them insubstantial alignment at all times.

The signals from the sensing heads 30 and 50 and the scanning station 20are communicated to processing computer 23 that provides operatordisplay and process control. Signals from computer 100 are sent toactuators 11 a to control the thickness of paper 12. Computer 100 andassociated actuators 11 a, sensing heads 30, 50 and scanner 12 are knownas a quality control system.

In order to provide a cost effective, simple and reliable means ofmeasuring web tension as well as caliper, a standard caliper sensor 60,known from the prior art and shown in FIG. 3, can in accordance with thepresent invention be provided with the additional features describedherein to measure web tension. Sensor 60 measures web thickness by meansof a pair of sensing planes 62 a, 62 b contacting the web or sheet 12from both sides, and includes a magnetic based measurement of thedistance for the sensing planes 62 a, 62 b in order to provide the webthickness.

Sensor 60 is mounted in a scanner (not shown in FIG. 3 but well known tothose of ordinary skill in the art such as scanning station 20 shown inFIG. 2 herein) that permits travel across the web 12 to measure a crossdirection (CD) thickness profile of the web 12. In order to providemeasurement of web thickness, appropriate sensor electronics 63 and acomputer 100 are added to convert magnetic sensing element signals andaccurately display process thickness units. Such a scheme is describedfor instance in the '720 patent.

FIG. 4 shows the prior art caliper sensor 60 with associated air supply66, 68 for the top and bottom caliper measurement, respectively. Valves66 a, 68 a and pressure regulators 66 b, 68 b allow for extension andretraction of the sensing planes 62 a, 62 b so that sensor 60 canmeasure the caliper of web 12. Not shown in this illustration areretraction springs or other devices that pull the sensing planes 62 a,62 b away from the sheet.

In accordance with the present invention, and as is described in moredetail in connection with FIG. 4, the air supply systems 66, 68 includeadditional features for alternate pressure selection for at least one ofthe sensing planes. The alternate pressure setting is utilized fortension measurement and is provided by the combination of valve 66 c andpressure regulator 66 d.

FIG. 4 also shows sheet guides 70, 72 before and after the caliper andtension measurement. These guiding devices 70, 72 can be distant from ornear the caliper measurement and may consist of rollers, sliding contactbars, or non contacting air bearings.

FIG. 5 shows the sensor 60 of FIG. 4 in a state where the alternatepressure settings are activated to allow web tension measurement. Thelower sensing plane 62 b is de-activated and retracted in the sensor.The upper sensing plane 62 a is activated with an alternate pressuresetting to permit a light touch deflection of the web 12. The pressurein upper half of sensor 20 is chosen to introduce a measuring gap 74between upper and lower sensing planes 62 a, 62 b that is significantlylarger than the web thickness, but yet introduces a measurabledeflection of the web 12. For instance, the web thickness on finewriting paper may be 0.1 mm, while the gap between the sensing elementsthat measure paper deflection is of the magnitude of 4 mm. In general,the measuring gap 74 between the sensing planes 62 a, 62 b should be atleast 10 times the thickness of the web 12.

The measuring gap 74 between the sensing planes 62 a, 62 b is indicativeof the sum of caliper and web tension effects. This distance is measuredby the same devices that measure caliper. If the thickness of the sheet12 is very small compared to the gap distance for sensing tension,caliper may be neglected. For caliper values that are larger, the mostrecent caliper profile may be subtracted from the tension measurement.

In the device illustrated in FIGS. 4 and 5, control commands from acomputer (not shown in either figure but typically the same as computer100 shown in FIGS. 2 and 3) are used to activate the sensing pressuresto, at user selectable intervals, alternate between caliper and webtension measurement mode. For example, the caliper profile may bemeasured during 20 scans across the web 12, followed by a measurement ofthe web tension profile for one scan, with this alternating measurementcontinuously repeated. The web tension CD profile is believed to haveless dynamic variability than the caliper CD profile, and thus it maynot need to be updated at a very high rate. Of course, user demand canalso be used to issue control commands that activate the sensingpressures to alternate between caliper and web tension measurement mode.

FIG. 6 shows an alternate method and apparatus for providing a computerselectable caliper and tension sensor air pressure. A continuouslyadjustable sensing pressure for each sensing plane is generated byproportional valves 80 a, 80 b under control of an associated signal 84a, 84 b from a computer (not shown here but typically the same as thecomputer 100 shown in FIGS. 2 and 3), and with an associated feedbacksignal 82 a, 82 b for closed loop pressure control. This method andapparatus has less parts than the air supplies 66, 68 shown in FIGS. 4and 5 and allows for a wide range of pressure settings that may beuseful for paper processes with a wide range of product thickness.

In another embodiment of the invention, two identical or similarmeasurement devices 90 a, 90 b may be installed in tandem to separatelymeasure caliper at device 90 b and tension at device 90 a as illustratedin FIG. 7. While not shown in FIG. 7, those of ordinary skill in the artwould understand that there are air supplies associated with the upperand lower sensing planes of sensor 90 b to simultaneously extend both ofthose planes to measure caliper of the moving web 12 and an air supplyassociated only with one of the two sensing planes of sensor 90 a toextend that plane to measure the tension of the moving web 12 withoutpinching the web.

The air supply associated with one sensing plane of sensor 90 a would beas shown in either FIG. 5 or 6 and measurement device 90 a includes asis shown in FIG. 7 the sheet guides 70, 72. This tandem arrangementenables a non-interrupted measurement of both caliper and tension but itadds cost and requires more room in the paper machine.

The fundamental tension measurement geometry is illustrated in FIG. 8.Consider a simple case where sheet 12 is thin, that is, printing gradepaper such as for example newsprint and fine writing paper, the verticaldeflection z is much larger than sheet thickness t, and the bendingresistance from sheet stiffness is much smaller than the deflectionresistance from web tension T. It is also assumed that the applied forceF(z) is constant and does not depend on z. The assumption of a constantforce for small deflections is reasonably well met with typical designsof the bellows or diaphragms activating sensing planes in a calipersensor, however a more complex model that includes a non constant forcevs. deflection of the bellows or diaphragms may be added for additionalrefinements. For the sake of simplicity of analysis it is assumed hereinthat the force is deflection independent.

The following simple geometry relation can then be derived for webtension T as a function of a constant vertical force F(z) and measuredvertical deflection z:T=F(z)/(1/(sqrt((L1/z)²+1))+1/(sqrt((L2/z)²+1)))This relation is illustrated in FIG. 9 for the parameters L1=200 mm,L2=100 mm, F(z)=1 Pa.

The influence of sheet bending stiffness is illustrated in FIG. 10. Thisdata was experimentally generated by applying a force on a paper samplewith the same configuration as in FIG. 9. One primary data point wasmeasured by the change in sag on an end supported 200 μm thick paper at300×300 mm size for a load F(z) using a small weight. The curve isextrapolated up and down from this point by using the textbook relationfor sheet bending deflection from a constant force:Deflection=k/(Paper thickness)³

This formula assumes a homogeneous sheet without any layering andconstant E-modulus. In reality, different paper types may deviate fromthis curve by ±50% or even more. The data thus should be used only fororder of magnitude error estimate.

By comparison of the modeling results in FIG. 9 and FIG. 10, it can beconcluded that for typical conditions of web tension and thickness, thebending resistance term may be neglected. For thicker paperboardproducts, for instance exceeding 150 or 200 μm, options exist to use abending stiffness compensation term from measured caliper, or to extendthe distance between the two sheet guides 70, 72. One extreme case ofdistance extension for very thick products includes elimination of oneor both sheet guides 70 or 72 and only utilizing the paper machineryrolls for web support on one or both sides of the sensor.

With anticipation of the main need for runnability measurement formainly thinner to medium thickness grades of paper, bending stiffnesseffects are not a main concern for the general usability of thisinvention.

Calibration of this sensor can be easily checked by placing a desireddimension sample strip through the sensor gap and pulling it by aconstant force by using weights that pull one end of the sample hangingoutside the sensor guide roll, and alternately measure caliper and webtension.

When measuring a web 12 of finite width, there will be edge effects onthe profile due to less of the web material participating in sharing thetension near the edge. This is true for any local tension measurementdevice applied to a web 12 and it also reflects conditions applicablefor roll building. A target profile may be generated for a suitableprofile shape including edge effects.

In paper making environments, the combination of caliper and tensioninformation across the web 12 may be utilized for improvedcharacterization of roll quality. This information can also be appliedfor improved automatic controls using existing web profile actuators.Additionally, the invention can be connected to communicate with a papermachine drive system, such as for example, controller 18 a and drivemotor 18 b of FIG. 1, or winder machine for improved tensioncharacterization and control to build more uniform paper rolls.

Although the embodiments in this description are related to contactingcaliper sensors the invention may also utilize air bearing based noncontacting caliper sensors. Furthermore, the invention is applicable toany web thin material including coated products or extruded plasticssheets.

It is to be understood that the description of the foregoing exemplaryembodiment(s) is (are) intended to be only illustrative, rather thanexhaustive, of the present invention. Those of ordinary skill will beable to make certain additions, deletions, and/or modifications to theembodiment(s) of the disclosed subject matter without departing from thespirit of the invention or its scope, as defined by the appended claims.

1. A method for measuring in a direction across a moving web bothtension and caliper of said moving web comprising: using a single sensorto measure tension and caliper of said moving web at a location on saidmoving web; providing support for said moving web before and after saidlocation on said moving web where said single sensor measures tensionand caliper of said moving web; and controlling said single sensor toalternate between two operating modes where in one of said two operatingmodes said single sensor measures caliper of said moving web and inanother of said two operating modes said single sensor measures tensionof said moving web.
 2. The method of claim 1 further comprising causingsaid single sensor to move transversely across said moving web.
 3. Themethod of claim 1 wherein said single sensor is controlled upon demandor at predetermined intervals to alternate between said two operatingmodes.
 4. The method of claim 1 further comprising controlling airpressure to said single sensor to thereby cause said single sensor toalternate between said two operating modes.
 5. The method of claim 1wherein said single sensor has first and second sensing planes onopposite sides of said moving web and said controlling said sensor toalternate between said two operating modes comprises extending in one ofsaid two operating modes both said first and said second sensing planesto measure caliper of said moving web and extending in the other of saidoperating modes only said first sensing plane to measure tension of saidmoving web.
 6. The method of claim 4 wherein said single sensor hasfirst and second sensing planes on opposite sides of said moving web andsaid controlling of air pressure to said single sensor further comprisescontrolling said air pressure in one of said two operating modes toextend both said first and said second sensing planes to measure caliperof said moving web and controlling air pressure to only said firstsensing plane to measure tension of said moving web.
 7. The method ofclaim 5 wherein said moving web has a predetermined thickness and saidsensor is controlled in said other operating mode to extend only saidfirst sensing plane to lightly touch said moving web to thereby deflectsaid moving web by an amount that is larger than said predetermined webthickness.
 8. The method of claim 4 further wherein said air pressure tosaid single sensor is adjustably controlled.
 9. A single sensor formeasuring in a direction across a moving web both tension and caliper ofsaid moving web at a location on said moving web comprising: means foroperating said single sensor to alternate between said calipermeasurement and said tension measurement.
 10. The single sensor of claim9 further comprising a guide for supporting said moving web eitherbefore, after or both before and after said location.
 11. The singlesensor of claim 10 wherein said guide for supporting said moving web isselected from rollers, sliding contact bars or non contacting airbearings.
 12. The single sensor of claim 9 further comprising: means formeasuring caliper of said web at said location on said moving web; andmeans for operating said caliper measuring means to upon demand or atselectable intervals alternate between said caliper measurement and saidtension measurement.
 13. The single sensor of claim 12 wherein saidmeans for measuring caliper of said web at said location on said movingweb comprises first and second sensing planes located on opposite sidesof said moving web, said single sensor measuring caliper of said movingweb when said first and said second sensing planes are both activatedand said means for operating said caliper measuring means to upon demandor at selectable intervals alternate between said caliper measurementand said tension measurement deactivates at said selectable alternateintervals a selected one of said first and said second sensing planes.14. The single sensor of claim 9 wherein said means for operating saidsingle sensor to alternate between said caliper measurement and saidtension measurement operates said sensor upon demand or at selectableintervals.
 15. The single sensor of claim 9 wherein said means foroperating said sensor to alternate between said caliper measurement andsaid tension measurement comprises means for providing controllable airpressure to said single sensor to thereby cause said single sensor toalternate between said caliper measurement and said tension measurement.16. The single sensor of claim 15 further comprising first and secondsensing planes on opposite sides of said moving web and said means forcontrolling of air pressure to said single sensor further comprisesmeans for controlling said air pressure in said caliper measurement toextend both said first and said second sensing planes and controllingsaid air pressure in said tension measurement to only extend said firstsensing plane.
 17. The single sensor of claim 13 wherein said moving webhas a predetermined thickness and said sensor is controlled in saidtension measurement to extend only said first sensing plane to lightlytouch said moving web to thereby deflect said moving web by an amountthat is larger than said predetermined web thickness.
 18. The singlesensor of claim 15 wherein said means for providing controllable airpressure is adjustably controlled.
 19. A method for measuring in adirection across a moving web both tension and caliper of said movingweb comprising: using two sensors in tandem to measure at a location onsaid moving web tension of said moving web by one of said two sensorsand caliper of said moving web by another of said two sensors.
 20. Themethod of claim 19 further comprising supporting said moving web beforeand after said tension measurement by at least one guide associated withsaid one of said two sensors.
 21. A system for measuring at a locationon a moving web both caliper and tension of said moving web comprising:a sensor for measuring caliper of said moving web in tandem with asensor for measuring tension of said moving web; at least one guideassociated with said sensor for measuring tension of said moving web tosupport said moving web during said tension measurement.
 22. The systemof claim 21 further comprising a first guide associated with said sensorfor measuring tension of said moving web before said tension measurementand a second guide associated with said sensor for measuring tension ofsaid moving web just after said tension measurement.
 23. A qualitycontrol system for a web making machine comprising: a scanning framehaving an opening through which a moving web passes; a sensor mounted insaid scanning frame for measuring at locations across said moving webboth tension and caliper of said moving web, said scanning frameoperable to cause said sensor to move back and forth across said movingweb; and means for operating said sensor to alternate between saidcaliper measurement and said tension measurement.
 24. A web makingmachine comprising: a system for controlling quality of said webcomprising: a scanning frame having an opening through which a movingweb passes; a sensor mounted in said scanning frame for measuring atlocations across said moving web both tension and caliper of said movingweb, said scanning frame operable to cause said sensor to move back andforth across said moving web; and means for operating said sensor toalternate between said caliper measurement and said tension measurement.